The treating agent is responsible for inhibiting scale formation and corrosion in the system equipment and also for inhibiting formation of deposits and for preventing settling of suspended solids (dispersancy) on the system equipment, in particular the heat exchanger. In this role, the agent is consumed.
The treating agent is added in a predetermined concentration ("standard") to the cooling water, a standard concentration determined initially as most probably adequate for preventing scaling, corrosion and deposits. There may be several treating agents combined in one dose but collectively or individually they enhance performance of the system equipment by forming protective films thereon (corrosion inhibitor) or by adsorption onto unwanted particles (e.g. CaCO.sub.3 and other scaling salts) to prevent their agglomeration or further growth, thereby preventing scale deposits of the system equipment.
As disclosed in my earlier patent, by including a known amount of an inert tracer (ppm fluorescent tracer, e.g. 2-naphthalene sulfonic acid, "2-NSA") with the treating agent, it is possible to measure and control the concentration of the treatment added to the system by measuring the emissivity of a sample of water and comparing it to the standard solution of the tracer. This is a highly accurate analysis because the fluorescent tracer is chosen s that it will not be affected by reaction with the system equipment (adsorption or deposition) nor will it react with any of the treating agents or natural impurities in the water. The tracer moves through the system as a discrete, unchanged entity as a true indicator of treatment concentration and characteristics of the cooling water system. Its integrity in other words is a constant, chemically and physically inactive with the system, although when calibrating the emissivity instrumentation it may be necessary to compensate for minor amounts of fluorescence which may be present in the system water (background fluorescence) or the treating agent.
In operation of a cooling tower, several important phenomena are involved: evaporation, "blowdown" to discharge collected impurities and replacement of the blowdown volume by "makeup" water.
Operating conditions may change (more or less blowdown for example) and as a consequence there may be a corresponding change in concentration of the inert tracer (and treatment dosage), determined by emissivity measure, calling for a higher feed rate of treatment when blowdown rate increases (an increased amount of untreated makeup water added to the system) and a lower feed rate of treating agent when blowdown rate decreases.
The inert tracer also serves as a diagnostic tool. Cooling tower systems are so complex that there are examples when the operators are not aware of system operations which are outside of specifications.
There are actually times when the chemical feed system (valve, pump, etc.) may fail or when unaccounted sources of makeup water enter the system. Such anomalies can be critical because clearly they change the treating agent concentration within the system which will be shown by changes in emissivity value of the inert tracer in the system water. Thus, an inordinate increase or decrease in blowdown from the system (or makeup water added to the system) will show up as an unexpected emissivity value as the system is sampled. When previous samples demonstrated that the system was operating properly, then unexpected changes in emissivity reading can serve as an indication of incorrect operation of the system and the cause of that incorrect operation.
Thus, if the emissivity reading of the inert tracer in the sample remains steady at a value corresponding to 100 ppm treating agent, then the concentration of treating agent is in conformance with the expected standard. But in the example of a volumetric change determined by an emissivity reading that does not compare to the standard dosage (e.g. 10 ppm decrease in treating agent concentration as determined by the inert tracer), then there is out-of-specification or non-standard operation of the system which requires an audit to identify and correct the incorrect operation of the system.
The foregoing presents a brief summary of the disclosure in U.S. Pat. No. 4,783,314. The entirety of that disclosure is incorporated herein by reference as constituting a known publication. In essence, use of an inert tracer enables volumetric changes in a circulating body of water to be detected with precision, the circulating body of water being one contained by or within the system equipment and one to which a treating agent is added and a portion of which will be consumed as it serves the role of inhibiting impurities likely to cause scaling, corrosion or deposit formation, any one of which can impair the efficiency of the equipment, especially the heat exchanger in a water cooling tower.